Multiple-effect solar still



I'uly 20, 1948. D. c. GINNINGS IULTI'PLE EFFEcT vsorhlm STILL Filed Dec. 2:5, 194s 2 Sheets-Sheet 1 I NVENT OR DeFoE C. Gum/N65 ATroRNEY July 20 1948. n. c. Gl'NNlNc-zs 2,445,350

HULTIPLE EFFECT sQLARfsTILL Filed Dec. 2s, 1943 2 sheets-sheet 2 iNvEN-ron DefoeBC. Glmvmss z8 ATTORNEY Patented `luly 2Q, 1948 UNITED STATES PATENT OFFICE amended April 30, 1928: 370 0. G '757) The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes without the payment to me of any royalty thereon in accordance with the provisions of the act of April 30, 1928 (Ch. 460, 45 Stat. L. 467).

This invention relates to an improved device for distillation, or more specifically, fox` using solar heat to distill sea water to obtain potable single plastic window, the plastic window and other underlying layers being broken away to disclose the underlying structure.

In these drawings (see Fig. 3), II represents a waterproof plastic window provided with means for inlating the same with air, here shown as a ilexible tube I2 which may be knotted at will to prevent the egress of air. A blackened water and vapor-proof iilm I3 is directly beneath the window I I and may be the underside of an inflatable bag, of which the window II forms the face and beneath the iilm I3 is an evaporator wick I4 hav ing an extension I5 for transferring a supply of sea water or other non-potable water to and water. l through the body of the wick, and one or more Prior to my invention, all solar stills of which extensions I6 protruding from the opposite man I have knowledge have been the single-effect gin of said wick I4. Directly beneath and in typethat is, the energy received from the sun Contact with the wick is a Water vapor transmithas been used only once for distillation. As a ting lm I1 and beneath the lm I1 is a non? result, efforts to devise solar stills which are apl wetting spacer I8, here shown as a large mesh plicable to emergency use in rubber life rafts screen having single strands in one direction have not been verysuccessful because the area, passing through loops of two twisted kstrands at Weight, and complications have been excessive in right angles thereto. Beneath the spacer Iii is proportion to the water obtainable from them. a layer of condenser cloth I9 having an exten It is an object of my invention, therefore, to sion '20 and underlying the main portion of thev devise a means of using the suns energy more `cloth I9 is a water and vapor-proof lm 2l.` 'hev than once to distill water, thereby greatly inwaterproof lilm 2I is in thermal contact with a creasing the amount of water obtainable from a second evaporator wick 22 of-a second still. The given area exposed to sunlight. extension I5 of the wick I4 is enclosed within. a It is a further object of my invention to devise 25 Water supply pocket 23 which may be closedby `a Va method of decreasing the Weight of the solar Zipper 24. The extension 20 of the condenser still to such a degree that its weight is small in cloth I9 projects into a distillate collectig pocket' comparison with the amount of water it can 25 which may be secured against spreading by distill in a reasonable period. stitching 26. The pocket 25 is provided withl ya` It is a, still further object of my invention to drain Outlet 21, here Shown as a knotted eXi'ble provide a solar still which occupies little space, tube. For securing my still against accidental either in storage or in use: has no rigid parts, loss while in use, such as by Wind or wave action, and requires the minimum of attention. I provide suitable means for lashing the device It has been the practice in multiple-effect stills in place such as cords 28 fastened by loops' 29. to distill in absence of air and vary the total Figure 2 discloses a section of a two-stagestill pressure of the distilling material from stage to having two spaced transparent windows1:the stage. However, the application of a solar still thicknesses of the layers being magnified for to a life raft practically excludesthe multipleclearness. Beneath the wick 22 (Figsz' and2) stage still with total pressure changing from'stage there are in order the Ivapor pervious fllm 30, the to stage. Therefore, a still has been devised in 40 non-wetting spacer 3|, the condenser cloth 32 and which the total pressure has been kept constant the water-and-vapor-Droof film 33, thus in this from stage to stage, while the partial pressure of second and succeeding stages the blackened layer water has been varied. and the plastic window are omitted because In the accompanying drawings: neither would assist in the efiicient use of the Figure 1 is an elevation partly in section, as it 45 heat passing through the rst still. may be positioned upon a rubber life raft; Figure 1 illustrates my method `of causing a Figure 2 is an enlarged section on the line 2-2 gradual liow of salt water from the supply pocket of Figure l, of a two-stage still having two spaced through 'the wick to flush out the concentrated transparent windows; .salts which would otherwise slow down the supply Figure 3 iS a Planf a tWO-Stage Still having a 50 0f water below the requirements of my still and .in time substantially stop the supply of water vapor.` This is accomplished by providing for a gravity assisted dischargeof concentrated salt water through the wick extensions I6 which are kept substantially lower than the supply of salt Water. In my multiple-stage still a single salt water pocket may supply water to a plurality of stills and the distillate may also be collected in a single distillate collecting pocket 25.

The basic principles of operation of my mult-iple-effect still are illustrated in Figs. 2 and 3.

In the first stage of this still, a source of heat H causes. distillation of water from I4 to an absorbent layer I9 on which the water condenses. The two absorbing layers I4 and I9 are separated by a non-wetting mesh spacer I9 which holds the two layers apart, but is mostly open to allow diiusion of Water vapor through air vfrom to I9.

The heat of condensation of the water on I9 in the first stage is transmitted to a second still through the waterproof layer 2 I to a. second layer 22 which is wet with salt water. This same heat causes distillation of water from 22 to a second condenser layer 32 (Fig. 2) which absorbs the water condensed in the second stage. A waterproof` film base 33 underlies the condenser layer 32.

The heat of condensation of the water in 32 of the second stage may similarly be used in a third stage, and as many stages as may be deemed practicable.

As an aid to keeping the spacer to a minimum thickness, it was found desirable,l 'but not necessary, to introduce between the absorbent layer I4 and the non-wetting spacer I8, the layer I1. This layer consists of a thin lm of a material such as regenerated cellulose which freely transmits water vapor, but which presents a reasonably dry surface next 'to the non-wetting spacer.

The theory of operation of the one stage of the still is as follows: The transfer of heat from the evaporator layer I4 to the condenser layer I9 is accomplished by distillation of water, and by radiation, conduction, and convection. The design of the still is such that the heat transfer by distillation is large in comparison with all other heat transfer. This allows a. high efficiency.

By making the distance between I4 and I9 small, the convective and radiant heat transfer become negligible in comparison with the heat transfer by distillation and by conduction. Theheat transfer by distillation is made large compared to that by conductionby several means.

First, the amount of solid material in the separator I8 between I 4 and I9 is kept to the minimum required for avoiding contact of I' and I9 is not too or bridging the gap by surface tension.. In this way the solid conduction is minimized.-

Second, the separator I9 and layer I1 are made as nonwetting as possible so that the liquid water does not bridge the gap between I1 and I9 by surface tension. In this way the liquid conduction is` minimized. ,l i

Third, the still is operated .at such a temperature f that the heat transfer by distillation is large 'in comparison with the heat transfer by` conduction through the air and other materials between the layers I1 and I9. Increase in the operational temperature ofthe still greatly increases the vapor pressure of water which causes distillation. However increase in temperature has only slight effect on the thermal conductivity of materials.

The use of the construction principles previously described, in a solar 'still to be used on rubber life rafts is shown in Figure 1. The still is supported by the rubber life 'raft tube 36. The suns rays H are transmitted through the plastic windows II and are absorbed on the black layer I3 (Fig. 3). The plastic windows with their intermediate air spaces transmit most of the suns energy to I3, but prevent.excessive loss upward of the heat produced at I3. These windowfaced bags maybe deilated to permit compact storage when not in use.

Layer I3, in addition to converting the suns rays to heat, is impermeable to both liquid and vapor water. The heat thus produced in I3 passes through the multiple-effect still, through the rubber life raft tube 36, and is eventually transmitted to the sea water and air. In passing through thev still, this heat produces distilled water in each of the stages in the manner previously described.

The sea Water is held in the pocket 23 and flows through the evaporator layers Min the still by capillary and syphon action. The top ends of the evaporator layers I5 from all the stages extend into the sea water pocket 23, while the bottom ends I6 Yextend down to a. lower level than the salt water supply to provide drainage of the concentrated sea water from the bottom ends I6. In thismanner, the formation oi' solid' salt in the evaporating layers in the still is avoided and the high efliciency of the still is maintained by providing a gradual discharge of concentrated salt water and maintaining during evaporation a sea water supply which concentrated.

The water distilled in the multiple-effect still is collected in the condenser layers I9 and flows by capillary and syphon action to the bottom end 20 of the condenser layer I9 into the pocket which holds the distilled water.

The -plan ofl the multiple-effect solar still is shown iriFigure 3. The still is assembled on a plastic i'llm base 33 indicated by full lines. A. pocket '23 is made in the top end to hold the sea water which is introduced by opening the zipper 24. A second pocket 25 at the bottom end is made to hold the distilled water.

The top'ends I5, of the evaporator layers- Il, consisting of textile material such as a thin flannel cloth, extend into pocket 23. The bottom ends, I8, of 'the evaporator'layers are shaped so that vthe concentrated sea water drains away from the center and drips off. The bottom ends, 20, of the condenser layers I9, also thin textile material, extend into the pocket 25 and are designedv to bring the distilled water to the center. A drain outlet 21 in the pocket 25 is in removing the distilled water.

' The evaporator and condenser layers are separated in each stage as shown in Figure 2 by a plastic screen spacer 3l, and a. layer 3l! of such material as. regenerated cellulose which freely transmits water vapor. Between successive stages is a thin layer of waterproof material such as Vinylite or Pliofllm which does not allow mixing of the condensed water in one stage with the sea water in the next stage.

On top of the assembly of the several stages of thev still are located the plastic windows. 'I'he space between these windows may be inflated while in use to conserve solar heat. The edges of these windows may be sealed to the plastic foundation of the still, thus forming one complete unit which may be rolled compactly for storage.

It should be understood that the present disclosure is for the purpose of illustration only, and -that the invention vincludes all modifications 'and equivalents which fall within the scope of the appendedy claims.

andato Itshould also be understood that my invention is not limited to the materials, dimensions or arrangement shown and described in my preferred embodiment of my still.` The spacer may be of any material which is relatively nonwetting. It is possible to use a textile material which has been treated to make it non-wetting. The regenerated cellulose layer may be eliminated entirely under certain conditions, or it may be replaced'by other materials having desired properties. For example, a material may be used which is permeable to` vapor, but which does not allow certain compounds to diuse through it.

The evaporator and condenser layers may be made of any material which serves to absorb the liquid and has the desiredv mechanical properties.

The ilexible windows should be made of a material which transmits the maximum amount of sunlight, but transmits the minimum amount of radiation from the black surface. The number of windows may vary to suit the particular application. It is even possible under certain circumstances to eliminate the windows entirely and work at reduced efficiency.

The black absorbing material may be incorporated in the evaporator cloth in the first stage instead o in the waterproof layer just above it,

The arrangement of the solar still is not limited to that shown in Figures 2 and 3. The arrangement shown is merely one application possible to a rubber life rait. The solar still may be used with a support as a sunshade `for the life raft, dissipating heat to the air or by evaporation of water. The sea water'does not necessarily go up by capillary action. It may travel entirely down through the still by action of gravity. Again, it is possible to extend the tops of the evaporator layers directly into the sea, keeping the bottom ends inside the raft at a level lower than the sea.

The application of the multiple-effect still described is not limited to use with solar energy. Any source of heat may be applied to, give multiple distillation. It is possible to turn the still over, having the evaporator layers below the condenser layers.

The number of stages which may be practical may be increased by providing interchange of heat of the distillate and sea water drainage with Y the input of sea water.

The multiple-effect still involving the principles described may also be used in the distillation of other materials, beside Water. In fact, it is more easily adapted'to materials having a lower normal boiling temperature than water, due to the increased heat transfer by distillation.

The multiple-effect still described may also be used for concentrating solutions, such as sugar or salt. The operation of all the stages at the same total pressure (atmospheric oiiers certain advantages over the usual method oi.' operating the stages at different total pressures.

I claim:

l. A multiple stage solar still comprising one or more aligned windows of ilexible transparent material, a light converting flexible waterproof partition in alignment with said windows and marginally sealed thereto, a liquid absorbent wick in contact with the underside of said partition provided with extensions beyond the margin of the partition, one extension adapted to draw non-potable liquid into the still, and another eX- tension adapted to discharge concentrated liquid by syphon action, a pocket for a supply-'of nonpotable liquid into which a portion of said wick layer extends, a screen under said absorbent layer, a second absorbent layer having an extension for directing the flow of distillate, a iiexible waterproof partition beneath said screen, a waterproof ilexible pocket for collecting said distillate, and one or more additional stills in thermal contact with said rst still and connected with said distillate receiving pocket. v

2. In a multiple stage solar still forproviding a potable condensate from non-potable water .the improvement which comprises an external vaporimpermeable enclosure, a layer ot liquid'absorbent material within said enclosure, a non-wetting vapor permeable` separator in contact with said absorbent material, a second layer of liquid absorbent material in contact with the face of said separator opposite to said first layer of absorbent material serving as a condenser for vapor passing through said separator, and a second vaporimpermeable enc-losure in contact with said condenser, a third layer oi.' liquid absorbent material in contact with said second enclosure, a second non-wetting vapor permeable separator in contact with said second absorbent layer, a fourth layer of liquid absorbent material in contact with said second separator serving as a second condenser, means for supplying non-potable water to said ilrst and third liquid absorbent layers, and means for collecting distillate from said condensers.

3. A multiple stage solar distillation apparatus comprising a heat absorbing layer, a plurality of flexible enclosures in thermal contact with each other, a layer of fluid absorbent material within each of said enclosures, a vapor absorbent layer in each enclosure a vapor pervious screen and a non-wetting spacer separating each heated uid supplied layer from a` cooler vapor absorbent layer,means for supplying liquid to said uid supplied layers, and means for collecting the condensate from said vapor absorbing layers.

A4. A exible distillation apparatus adapted to utilize solar heat intercepted by a heat absorbing flexible layer and having an inflatable heat applying enclosure, the improvement which comprises a plurality of superimposed ilexible enclosures. a iluid absorbent wick with a discharge extension within an enclosure in thermal contact with said heat applying enclosure, an absorbent condensing -layer within a second enclosure, a vapor pervious screen and a non-wetting spacer separating said absorbent and condensing layers,

means for supplying non-potable liquid to said absorbent layer, and means for collecting the condensate from said condensing layer.

5. A flexible distillation apparatus adapted to absorb and utilize solar heat having a heat applying enclosure and a heat'intercepting layer, the improvement which comprises a plurality of superimposed flexible enclosures each in thermal contact with each adjacent enclosure, a fluid absorbent wick with a discharge extension within an enclosure in thermal contact with said heat applying enclosure, a vapor pervious screen in contact with said wick, a non-wetting spacer, an

absorbent condensing layer in contact with said non-wetting screen wall, a second wick having a discharge extension in thermal contact wlththe side of said condensing layer remote :from said first wick, a iiexible receptacle for supplying nonpotable liquid to said wicks, and a ilexible distillate collecting receptacle.

6` A multiple 'stage solar distillation apparatus comprising a plurality of flexible enclosures in each thermal contact with a successive enclosure. the first of said enclosures being inflatable and having a solar heat absorbing layer, a vapor pervious screen and a non-wetting separating spacer in each enclosure, an absorbent wick with a discharge extension in the heated side of each of said enclosures and a layer of vapor absorbent material in the cooler side of each enclosure. a pocket for supplying non-potable water to each of said wicks. and a pocket for collecting and holding distillate from said condensing layers each vapor condensing layer serving to transmit heat to a succeeding enclosure.

- DEFOE C. GINNINGS.

REFERENCES CITED The following references are of recordin the ille of this patent:

8 UNITED sTATEs PATENTS Number 15 Number Name Date. Theisen Dec. 31. 1895 Van Brunt Feb. 26, 1929 Dooley June 30, 1931 VBenjamin Oct. 4, 1932 Payne l., May 15, 1934 Hickman May 17, 1938 Waterman May 23, 1939 Delano June 25, 1948 Miller Dec. 10, 1946 Delano Dec. 24, 1946 FOREIGN PATENTS Country Date Great Britain 1889 France Jan. 27, 1930 lNorway June 25. 1923 

